The present invention relates to a laser surveying instrument for forming a horizontal plane or a tilted plane as desired by projecting a laser beam by rotary irradiation.
Reference lines and reference planes are indispensable in the execution of construction work and civil engineering work, and the reference line and plane are formed as the result of projection of the laser beam by rotary irradiation. In the past, a laser surveying instrument has been known, which can form a horizontal reference plane and also can form a tilt reference plane with a desired tilt angle, and such surveying instrument is described in JP-A-6-26861 or in JP-A-2001-280964.
The laser surveying instrument 10 as disclosed in JP-A-6-26861 comprises, as shown in FIG. 5, a projector 1 for projecting a laser beam 13 by rotary irradiation and tiltable in two directions, 2 sets of tilting mechanisms 2 for tilting the projector 1 in two directions, 2 sets of fixed tilt detectors 4 provided on a plane 3 crossing perpendicularly the axis of the projector 1 and for detecting tiltings in two directions, 2 sets of tiltable tilt detectors 6 crossing the axis of the projector 1 and arranged on a tiltable plane 5 which is enabled to tilt in two directions, and 2 sets of tilt setting mechanisms 7 for tilting the tiltable plane 5 in two directions.
In case that a horizontal plane is to be formed, the tiltable tilt detector 6 is aligned with the fixed tilt detector 4 so that the fixed tilt detector 4 indicates horizontal direction and the tiltable tilt detector 6 indicates horizontal direction. The projector 1 is leveled so that the fixed tilt detector 4 and the tiltable tilt detector 6 detect horizontal direction, and a horizontal reference plane is obtained by projecting the laser beam 13 from the projector 1 by rotary irradiation.
In case that a tilt reference plane is to be formed, the tiltable tilt detector 6 is tilted by the tilt setting mechanism 7 based on the fixed tilt detector 4 as a reference. Tilting of the tiltable tilt detector 6 can be attained when the tilt setting mechanism 7 gives mechanical displacement to the tiltable plane 5.
By leveling the projector 1 by means of the tilting mechanism 2 in such manner that the tiltable tilt detector 6 which was tilted indicates horizontal direction, the projector 1 can be tilted in a direction as desired. And by projecting the laser beam 13 from the projector 1 by rotary irradiation, a tilt reference plane can be obtained.
The laser surveying instrument 15 disclosed in JP-A-2001-280964 comprises, as shown in FIG. 6, a projector 1 for projecting a laser beam 13 by rotary irradiation and tiltable in two directions, 2 sets of tilting mechanisms 2 for tilting the projector 1 in two directions, a first tilt setting unit 8a provided on the projector 1 and capable to set a tilt angle of a first direction with respect to the projector 1, and a second tilt setting unit 8b (not shown) provided on the projector 1 and capable to set a tilt angle of a second direction perpendicularly crossing the first direction with respect to the projector 1.
The first tilt setting unit 8a comprises a first tilt angle detector 9a, first tilt sensors 11a and 12a, and a first tilt setting mechanism 7a for tilting the first tilt angle detector 9a. Also, the second tilt setting unit 8b comprises a second tilt angle detector 9b (not shown), second tilt sensors 11b and 12b (both not shown), and a second tilt setting mechanism 7b (not shown) for tilting the second tilt angle detector 9b. 
In case that tilt setting is performed by the laser surveying instrument 15, an angle detected by the first tilt angle detector 9a is tilted in opposite direction with the same numerical value as the set angle by the tilt setting mechanism 7a. Next, the projector 1 is tilted by the tilt mechanism 2 so that the first tilt sensor 11a detects the horizontal direction. By setting a condition where the first tilt sensor 11a detects horizontal direction, the setting of the tilted plane is completed.
However, in the laser surveying instrument of the former case, the tilt setting mechanisms are needed respectively for two tilting directions, and the mechanism has complicated structure. Further, the accuracy of the setting of the tilt angle depends on mechanical accuracy of the mechanical components. There is a problem that the accuracy of the setting angle may be affected, when mechanical components are worn out and the like as time elapses.
In the laser surveying instrument of the latter case, the setting of the tilt angle is performed by a tilt angle detector. As a result, the accuracy of the setting of the tilt angle depends on the mechanical accuracy of the mechanical components. And the decrease of the setting accuracy due to wearing and the like can be avoided. While problems lie in that complicated mechanism is required because tilt setting mechanisms are needed for two tilting directions respectively.